A touch screen is a user interface that covers a display and enables a user to operate a device simply by touching various locations on the touch screen. The touch screen is clear, so the user can view the display through the touch screen. The display shows information that enables a user to control the device by touching various locations on the touch screen. For example, the display may show various buttons that are associated with certain commands. When the user touches an area on the touch screen over the button, the device executes the command associated with that button. The device typically includes custom applications that enable the device to receive inputs from the touch screen. The touch screen may be sensitive to the touch of a finger, stylus, or other pointing device.
Touch screens typically include a laminate of at least two films with conducting internal surfaces and an array of spacers. Pressure on a surface of the touch screen decreases the resistance of the laminate at the point of pressure, thereby enabling the electronic detection of the location of the point of pressure. Thus, the location of a finger or stylus being used to touch the screen can be determined.
A touch screen may be used with display for a personal computer, such as a cathode ray tube (CRT) monitor. Additionally, a touch screen may be used with a portable device such as a laptop computer or a personal digital assistant (PDA). Laptop computers and PDAs typically utilize liquid crystal displays. Newer types of displays that may be used with PDAs and other portable electronic devices include organic light emitting diodes (OLEDs) and electronic ink.
LCDs require that a fixed amount of space be maintained between two glass plates that surround the shell of the liquid crystal. If pressure is applied to either of these plates, the image displayed on the LCD may be distorted. This phenomenon is typically referred to as bruising. Distortion of the image displayed on the LCD is detected around the area where pressure is applied. If sufficient pressure is applied to either of the glass plates, permanent damage to the cell may occur.
Because touch screens typically require an applied pressure to determine the location of a pointing device, and because LCDs are sensitive to applied pressure, a touch screen that is used with an LCD must be mounted on a separate piece of glass that is suspended some distance from the LCD. FIG. 1 illustrates a touch screen display 100 including a touch screen 102 suspended above an LCD 104 according to the prior art. Touch screen 102 includes a glass substrate 106, to which a touch screen system 108 is attached. Glass substrate 106 provides rigidity to touch screen 102. Touch screen system 108 may be laminated to the surface of glass substrate 106. LCD 104 includes a first glass plate 110 and a second glass plate 112. A liquid crystal display element 114 is located between first glass plate 110 and second glass plate 112.
Since liquid crystal display element 112 is sensitive to pressure, an air gap 114 must be maintained between touch screen 100 and LCD 102. Glass substrate 106 prevents touch screen 102 from coming into contact with LCD 104 when pressure is applied to touch screen system 108. However, the presence of glass substrate 104 and air gap 114 results in increased weight and bulk of the device on which the display is used. Furthermore, glass substrate 104 may reduce optical performance due to increased reflections from internal surfaces.